In modern data telecommunication systems, the receiver generally comprises an analog input amplifier stage coupled to analog-to-digital converter (ADC), the output of the ADC being provided to a digital signal processor (DSP).
The ADC generally has a limited input range and it is the role of the input amplifier stage to dynamically adjust the voltage of the input signal such that the ADC always receives a signal within its operating voltage. A problem is that the input signal in certain telecommunication systems can vary greatly in amplitude. The amplitude can, for example, depend on the distance between the telecommunication equipment and the transmitter and objects between the equipment and the transmitter, such as buildings etc. For example, in mobile telephone networks, mobile telephones which are closer to a telecommunications mast receive much higher signal strengths than mobile telephones which are very close to the edge of a network cell, very far from the mast. Furthermore, reception can be strong above ground, but weak below ground.
It has been proposed to use a variable gain amplifier (VGA) to dynamically adjust the input voltage to the correct level for the ADC. However, where a wide range of input voltages are possible, such a circuit is difficult to implement. Furthermore, it is slow to respond to input voltage changes, and has high power consumption.